Method of reducing sandiness in vinyl coatings

ABSTRACT

A method of reducing sandiness in a vinyl coating produced by a heat fusion coating process. A soluble organic tin compound is included as a component of the vinyl coating composition.

I United States Patent 1151 3,640,747 Richart 1 Feb. 8, 1972 54 METHOD OF REDUCING SANDINESS 3, 32,730 3/1362 K 1 2: ..117/21 VINY COATINGS 3, 7 ,0 2 1 1 6 R11: 11.... ..117/21 IN L 3,025,267 3/1962 Calfee 117/128 4 [72] Inventor: Douglas Steven Richart, Berks County, Pa. 3,072,597 1/ 1963 Lavin et a1. 17/232 3,137,666 6/1964 LOX et a1. ..l17/132C [73] Assgnee- The Readmg 3,247,167 4/1966 Jason at al ..117/132 c [22] Fi1ed: Sept. 12, 1968 3,313,760 4/1967 Barnes et a1. 17/232 3,313,761 4/1967 Barnes at 111.... ..117/232 1 1 pp 1 9 3,350,332 10/1967 Hardy a a1. ...1 17/ 128.4 Related USl Applicauon Data 3,376,246 4/ 1968 Valentme et a1 ..1 17/132 C [63] Continuation Of $61. No. 528,366, July 18, 1966, hammer-William Martin abandone Assistant Examiner-Raymond M. Speer I Attorney--Synnestvedt & Lechner [52] US; Cl. .'.....l17l2l, 117/128.4, 117/132 C,

Y 117/161UZ, 117/1611-1,117/161UF, 117/232 [571 ABSTRACT [51] Int. Cl. ..B44d l/094, 344d l/46 A method of reducing sandiness in a vinyl coating produced [58] Field of Search ..1 17121, 128.4, 161 U, 161 UH, by a heat fusion coating process. A soluble organic tin com- 117/232, 132 C pound is included as a component of the vinyl coating composition.

[56] References C1ted 3 Claims No Drawings UNITED STATES PATENTS V I 7' i m 3,136,6516/1964 Spessard .....117/21 METHOD OF REDUCING SANDINESS IN VINYL COATINGS This application is a continuation of application Ser. No. 528,366, filed July l8, 1966, now abandoned.

This invention relates to the reduction of sandiness in vinyl coatings. Specifically, it relates to the use of an organic tin compound in a vinyl coating composition.

As a class, the vinyl resins constitute one of the more important synthetic resinous materials useful in the fabrication of articles and in the application of protective and decorative coatings to base materials. Their importance results from a combination of excellent features of which the following are representative: they are tough, durable, and fairly resistant to chemical attack; they are relatively inexpensive as compared with other resins having comparable properties; and they conveniently may be used in almost any of the common plastic fabrication techniques.

It should be understood that as used herein, the term vinyl resins" is meant to include the various polyvinyl chlorides as well as copolymers of polyvinyl chloride, mixtures of polyvinyl chloride and polyvinyl chloride copolymers, and mixtures of any of the above with minor portions (e.g., less than 20 percent) of other resin systems. Examples of these copolymers are copolymers of vinyl chloride and vinyl formate, vinyl acetate, vinylidenc chloride, vinyl alkyl ethers, maleic esters, fumaric esters, acrylic esters, or acrylonitrile. Examples of the other resin systems referred to are hydrocarbon resins, acrylics, rosin esters, abietic acid, abietic acid derivatives, and the like. Thus, while the term vinyl will ordinarily be used herein for convenience, it is to be understood that it includes the above copolymers, mixtures of copolymers, and mixtures including other resin systems.

The vinyl resins with which this invention is especially concerned are the medium high to high molecular weight vinyls. These medium high to high molecular weight vinyls may be defined as those having a minimum specific viscosity of about 0.33 as determined by ASTM test Dl243-60, method B, and are desirable for use in coating compositions if special properties, such as deformation under load, are important. An example of such an application is the coating of dish racks for use in automatic dishwashers. The coating on these wire baskets must not only bear up against point contact with heavy plates and kitchen utensils, but it must do so at elevated temperatures extending to 250 F. and above.

In preparing vinyls for use in heat fusion processes, it is conventional to formulate them with other materials such as plasticizers, stabilizers, filler materials such as pigments and extenders, and the like. When so formulated and reduced to a dry, free-flowing, pulverulent state, these coating materials may be used in the various heat fusion coating processes including, for example, flame spraying, electrostatic spraying, dusting, cloud chamber, fluidized bed coating, and the like. These coating processes are similar to each other in that the coating materials are distributed over a substrate while in pulverulent form and then caused to flow out and fuse into a continuous coating layer by heating the coating materials to above their melting point. It is readily apparent that these heat fusion processes are distinct from those vinyl forming processes wherein both heat and pressure are relied upon to cause the vinyl to flow, such as calendaring, pressure casting and extrusion, as well as from those vinyl coating processes wherein the coating material is distributed over the substrate while in the form of a liquid, such as a plastisol or an organisol.

In order to provide heat to cause the pulverulent coating materials initially to adhere to the substrate and then fuse into a continuous protective layer, it is conventional to heat the substrate to a temperature above the melting point of the coating materials prior to contact therewith. This is known as preheating. In some instances, in order to complete the fusion of the coating materials after they have been distributed over the surface of the heated substrate, it is necessary to provide additional heat. This is known as postheating." It canreadily be understood that the need for postheating will depend to a large degree upon the mass and heat capacity ofthe substrate. For example, a coating applied to a thick-walled iron pipe might not require postheating whereas a coating applied to wire goods well might. Also, in the special case of electrostatic spraying coating processes, the finely divided coating materials are frequently distributed over a cold substrate by means of electrostatic forces and then the finely divided materials adhering to the substrate are caused to flow out by heat applied solely in a postheat oven.

When using the above described medium high to high molecular weight vinyls in heat fusion coating processes that require postheating, a condition known as sanding" is frequently observed. This condition may be defined as the occurrence of infusible particles that appear in the form of small granules or sandlike particles on the surface of thefinished coating. Once formed, these small sandlike particles are believed to be infusible since they no longer will fuse or flow out even at temperatures greatly in excess of the melting point of the coating materials. To this extent, they are clearly distinguishable from so-called sugar coatings" that are somewhat similar in appearance but which will fuse and flow out into a smooth layer by further heating of the coating in a postheat oven. To repeat, no matter how much heat is applied, a sandy surface will not flow out into a smooth layer. A sandy surface is commercially.undesirable since it detracts from the appearance of the coating, the roughened surfaces will collect dirt and may be hard to clean, and the roughened surface may cause abrasion when brought into contact with various other articles.

Accordingly, it is the object of this invention to provide vinyl coating compositions that are substantially free from sanding when used in heat fusion coating processes.

Briefly, this and other objects of this invention are achieved by the proper selection of the stabilizer that is used in formulating the vinyl coating composition. Particularly, it has now been discovered that sandiness may be substantially avoided if stabilizers are selected from those in which the metallic component of the stabilizer is tin or other similar metal such as germanium.

While the exact nature and causes of the occurrence of sandiness are not understood, it has been observed that the tendency to develop a sandy surface is intensified when a number of coated substances are simultaneously placed in a postheat oven. For example, if a single substrate is coated with finely divided particles and the fusion is completed in a postheat oven, sandiness generally is not observed. However,

when a number of similarly coated parts are placed in thesame postheat oven all at the same time, it is not unusual for sandiness to develop. For this reason, it has been theorized that gaseous products may be evolved from the surface of the coating materials while they are detained in the postheat oven, which gaseous products may then react with other ingredients of the coating material to form localized areas of infusible particles. While the nature of the hypothesized gaseous products have not been identified, it now has been discovered that if such products do indeed exist, they apparently react with, or are catalyzed in their action by, the presence of certain stabilizers included in the formulated vinyl coating resins. This is substantiated by the discovery that vinyl coating materials that are quite subject to sanding will not sand if the stabilizer is removed therefrom. It can be appreciated that this does not present a practical solution to the problem since it is essential to use stabilizers in commercial vinyl formulations to prevent unduedegradation.

It has now been found that the occurrence of sandiness can be avoided if the stabilizer used in formulating the vinyl coating materials isan organic or inorganic salt of tin or similar element such as germanium. Conversely, when other common stabilizers known to the art such as those based upon lead, barium, cadmium, calcium and zinc, are used, it is often difficult to avoid the formation of sand.

In the following examples illustrating the utility of this invention, a vertical baffle was placed in a central portion of a standard electrically heated forced circulation convection oven. This baffle divided the oven into two'separate parts which could communicate through a small 4 inch square window located at a central portion of the baffle. Due to the nature of the forced circulation through the oven, the baffle divided the oven into an upstream and downstream portion so that gases could be circulated from the upstream portion of the oven, through the window, and into the downstream portion. The oven was then heated to a temperature of 450 F., and a gas velocity of L400 to L600 ft./min. was established therein.

Six substrates were coated in the fluidized bed coating process with a standard vinyl coating composition as described below and were hung in the upstream side of the oven. Specimens to be tested were. then preheated to 550? F. and dipped in a coating composition having the composition indicated in the examples for about 5 seconds to deposit a 12 to 15 mil coating over their surfaces. After the specimens were removed from the fluidized bed, they were immediately placed in the downstream side of the oven exactly 4 minutes after the six coated substrates had been placed in the oven. The specimens were allowed to remain in the oven under these conditions for 1 minute. These experiments were then repeated after the six coated substrates had been retained in the mentor 6, 8, l0, l2, and i4 minutes. By this means, the occurrence of sandiness was greatly accelerated and intensified due to the fact that any gaseous products evolved from PVC resin having a minimum specific viscosity of 0.33 as determined by ASTM test Dl243-60, method B Di-moctyl-n-decyl phthalate Epoxidized soya Tio CaCO, (pigment and filler) Barium-cadmium stabilizer (Mark W5) Organic chelating agent (Mark C) The test specimens were coated with an identical vinyl composition with the exception that the barium-cadmium stabllizer and the organic chelating agent were substituted for by the stabilizers as shown' in the following table. Examples XIV .and XV were performed separately from-the other experi- 25 ments and slight experimental variances are responsible for the differences between example ii and Example XV. The

results are indicated in the table as follows;

Time in minutes that coated substrates were Stabilizer in oven prior to introduction oi test specimens Trade Examples Type Designation Amount 4 6 8 10 12 14 No stabilizer used 0 0 0 0 0 0 ws 6 g H H H H u H 10 H H H H H H 8 S S 8 SIM SIM SIM 8 S S S S/ M SIM SIM Mark 33 8 S M H H H H Advastab CZ-11- 6 S M H H H H Mark X 4 0 0 0 0 0 0 Advastah T-360..- 2 0 0 0 O 0 0 Advastab lM-ISO... 4 0 0 O 0 0 O Advastab I150. 4 0 0 0 0 0 0 Advastab T270. 2 0 0 0 0 0 0 Advastab T-5 4 0 0 0 0 0 0 Mark 1038 4 0 0 U 0 0 0 iifiii 3} 0 0 s H H 0 None-N0 sandiness can be detected.

observation.

Slight-Sandiness can be detected by loci and M M0dornteSundinoss can be observed without dilliculty both 11 Heavy-sandiness causes the coating to close visual inspection.

by feel and visual inspection. be very rough to the touch and is markedly present by visual The various stabilizers used in the above examples are identified as follows:

Sold by the Argus Chemical 00:

utyl tin (lilnumtn.

Hold by the Advance Olimnicnl (.10.:

Arivttstnb 'l-3o0-n solid or nno-tin sulfur-containing or uno-tin complex con Advastab TMISFB li ul compound. aining no sulfur.

Advastub CZ-ilA-a so id calc um-zlnc organic complex. Advsstab 'I-5a liquid or ano-tin complex containing no sulfur. Advastab T270a solid d cctyl-tin sulfur containing compound. Advastab 'l150a dibutyl tin modified maleate ester.

Sold by Nuodex:

Nuostsb V-IOOB-a liquid organic barium-cadmium complex.

Sold by the National Lead 00 Tribase the six coated substrates were caused to flow through the window and impinge directly upon the specimens. Due to the intensified nature of this test, evaluation of the coating material for its susceptibility to sanding was greatly facilitated.

lt will be noted that the degree of sandiness tended to increase when the six coated substrates were detained in the oven for a longer period of time. This would seem consistent EXL-a modified basic lead silicate/sulfate. Dythal XL-a dibasie lead phthalate.

It will be noted in the above examples that the six substratesused to produce the gaseous products were coated with a vinyl be certain that it was not the stabilizer gf t he coating composition that was releasing the undesired gaseous products, the above experiments were repeated by variously using lead, tin, and calcium-zinc stabilizers for the coating compositions that with the theoretical basis for this invention, as the longer the 75 were used to coat such six substrates. in all of these experimerits, substantially the same results were noted as in the above examples.

I claim:

1. in a heat fusion coating process requiring a post heating step for coating an article using a dry vinyl resin composition comprised of vinyl chloride homopolymer or copolymers thereof with other vinylic monomers, the improvement comprising including a stabilizer consisting essentially of a soluble organic tin compound which is a stabilizer for vinyl resins in said composition, in an amount'effective to reduce sandiness in the heat-fused coating.

2. The method of claim 1 wherein the article to be coated is substantially fabricated from wire. 

2. The method of claim 1 wherein the article to be coated is substantially fabricated from wire.
 3. In a heat fusion coating process requiring a post heating step for coating an article using a vinyl resin composition comprised of polyvinyl chloride, copolymers of vinyl chloride, mixtures of polyvinyl chloride and vinyl chloride copolymers, or mixtures of these polymers with less than 20 percent of another resin, a method of reducing sandiness in a coating produced by said process comprising including a soluble organic tin compound which is a stabilizer for vinyl resins in said composition. 